Borderline Personality Disorder (BPD) is the most prominent and well recognised of all current personality disorder (PD) categories. However, it has not always been this way. In fact, the ‘borderline patient’ is one of the newer categories in personality classification. The term emerged, largely in North America, in the 1950s. While most ‘psychopathic’ personality types have been recognised in one form or another since the nineteenth century, borderline has not. Schneider’s (see Chapter 1) classification, which formed much of the basis for the DSM II and ICD 9 classification of personality, describes an ‘emotionally unstable personality’, but this is largely related to unstable mood and better translated as ‘with labile mood’ (Stimmungslabile). ‘Explosive personality’ shares some features with BPD but these are confined to disinhibition. Kraepelin expanded pathological personalities to seven types in the eighth edition (1909–15) of his textbook, but only one – ‘The Excitable’ (die Erregbaren) – has any overlap with BPD.